Estimates of New HIV Infections in the United States, 2006-2009

In August 2011, the Centers for Disease Control and Prevention released new estimates of the annual number of new HIV infections (HIV incidence) in the United States. The estimates, for 2006 through 2009, are the first multi-year estimates using CDC's national HIV incidence surveillance methodology, which is based on direct measurement of new HIV infections using a laboratory test (the BED HIV-1 Capture Enzyme Immunoassay) that can classify new diagnoses as either recent or long-standing HIV infections. The estimates were published online in the scientific journal PLoS ONE (http://dx.plos.org/10.1371/journal.pone.0017502).

The new estimates suggest that overall HIV incidence in the United States has been relatively stable at approximately 50,000 annual infections between 2006 and 2009. Each year, the largest number of new HIV infections was among white men who have sex with men (MSM)* followed closely by black MSM. Hispanic MSM and black women were also heavily affected. Over the four year period, new HIV infections appear to be relatively stable among all populations except young MSM. The overall increase among young MSM was driven by a 48 percent increase in HIV infections among young black MSM during the four-year time period.

In addition to providing the first estimates for 2007, 2008 and 2009, CDC has updated its earlier estimate of HIV incidence for 2006 (previously 56,300). The new, lower estimate reflects refined research methods and more data available due to reporting delays. While these HIV incidence estimates are based on the best data currently available, CDC will continue to refine estimates over time as improvements in methods or additional data are available.

Announced in July 2010, the National HIV/AIDS Strategy calls for prioritizing prevention efforts in the populations where HIV is most heavily concentrated -- gay and bisexual men of all races and ethnicities, African Americans and Hispanics/Latinos -- and for alleviating racial and ethnic disparities. To achieve the strategy's goals, CDC is implementing "High-Impact Prevention," a new approach designed to maximize available HIV prevention resources and have the greatest impact on the U.S. HIV epidemic.

Figure 1: Estimated New HIV Infections in the U.S., 2009, for the Most-Affected Subpopulations

Implications of New Estimates

The current level of HIV incidence in the United States is likely not sustainable. Prevention efforts in recent years have successfully averted significant increases in new HIV infections, despite the growing number of people living with HIV and AIDS who are able to transmit the virus. However, an analysis by CDC and Johns Hopkins University researchers indicates that the growing population of people with HIV and AIDS will lead to significant increases in new HIV infections if current prevention efforts are not intensified. The study emphasizes the importance of ensuring that everyone with HIV knows their status and helping HIV-infected individuals avoid transmission to others.1

The increasing number of new HIV infections among young, black gay and bisexual men underscores the importance of reaching young MSM with effective HIV prevention programs, and developing new programs that specifically address the needs of young, black gay and bisexual men. In addition, public health and community leaders can help reduce the stigma that too often surrounds HIV. This includes encouraging frank discussions about HIV and the factors that can contribute to the spread of the disease, such as unsafe sexual or drug-using behaviors, homophobia, higher rates of STDs and lower awareness of HIV status.

Key Findings: A Closer Look

Data Suggest Overall HIV Incidence Relatively Stable

CDC estimates that there were 48,600 (Confidence Interval [CI]: 42,400-54,700) new HIV infections in the United States in 2006, 56,000 (CI: 49,100-62,900) in 2007, 47,800 (CI: 41,800-53,800) in 2008 and 48,100 (CI: 42,200-54,000) in 2009.

The new estimates update CDC's original HIV incidence estimate for 2006 (previously 56,300 [CI: 48,200-64,500]). The new lower estimate reflects refined statistical modeling and the addition of data now available due to reporting delays (see Methods box below for additional information). CDC will continue to add new data and improve its research methods over time. As a result, HIV incidence estimates may continue to be refined in the future.

Methods for Estimating National HIV Incidence

CDC's latest estimates come from an HIV incidence surveillance methodology that is based on an approach known as STARHS (Serologic Testing Algorithm for Recent HIV Seroconversion). STARHS uses a special test (the BED HIV-1 Capture Enzyme Immunoassay) that classifies newly diagnosed infections as either long-standing or recent (occurring within approximately the past five months).

Before this surveillance methodology was developed, HIV diagnosis data provided the best indication of recent trends in key populations. However, diagnosis data does not indicate when an individual was actually infected, because infection can occur many years before a diagnosis. By applying the STARHS technology to new HIV diagnoses in 16 states and two cities, CDC identified the number of new diagnoses in a given year that represented new infections. Using a complex statistical model, these data were extrapolated to the general population to provide national estimates of HIV incidence based on direct measurement.

The new estimates represent the first multi-year estimates from this new HIV incidence surveillance methodology. CDC refined the previous statistical model to re-estimate HIV incidence for 2006, and provide the first estimates for 2007, 2008 and 2009. The updated model:

Revises the way in which HIV diagnosis data are adjusted due to reporting delays

Provides a more accurate way of estimating the probability that an infection would be detected when it is recent

Provides a more sophisticated process for determining transmission category data when that information is missing

Uses more recent data that allowed recalculation of the recency period of STARHS, which resulted in a revised period of time in which an HIV infection is considered to be recent

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